Abstract: :
Purpose: To investigate the relative contributions of Cl–channels and transporters to a circulating flux of chlorideions which has been implicated in the control of lens volumeand transparency.Methods: Organ cultured rat lenses and isolated fiber cellswere exposed to various Cl– transport inhibitors undereither isotonic or hypotonic conditions. In whole lenses theeffects of inhibitors on cellular morphology were determinedby confocal microscopy. In isolated fiber cells the effectsof inhibitors and osmolarity on membrane conductance and cellvolume were monitored by whole cell patch clamping and videomicroscopy, respectively.Results: The incubation of lenses in the presence of the KClcotransporter inhibitor, DIOA, produced peripheral cell swelling,while the addition of the Cl– channel inhibitor, NPPB,caused extracellular space dilations between deeper fiber cells.These results suggest that the influx and efflux pathways forCl– are different, spatially separated and change duringthe course of fiber cell differentiation. Consistent with thisview, fiber cells isolated from different areas of the lenscortex exhibited differences in Cl– conductance, and theability to undergo a regulatory volume decrease (RVD). Underisotonic conditions short peripheral fiber cells (<50µm)tended to have a minimal Cl– conductance, but upon exposureto a hyposmotic solution were capable of a RVD that was inhibitedby DIOA. Interestingly, exposure of short fiber cells to hyposmoticsolutions plus DIOA caused cell swelling and the subsequentactivation of a Cl– conductance. In contrast longer fibercells (>120µm) were dominated by an outwardly rectifyingCl– conductance which was blocked by NPPB.Conclusions: In young peripheral fiber cells Cl– effluxis mediated by KCl cotransporters, while in older deeper fibercells Cl– influx occurs via a conductive pathway. Sincefiber cells are connected by gap junction channels it is expectedthat the spatially distinct Cl– influx and efflux pathwayswill produce a circulating flux of Cl– ions. This impliesthat the maintenance of lens cell volume and transparency iscritically dependant on the interplay between anion channelsand transporters.